Optical inspection systems inspect a wafer by illuminating the wafer's surface, collecting light that is scattered or reflected from the wafer's surface, and detecting the scattered or reflected light by light detectors.
The illumination can involve scanning the wafer's surface by a single light beam, by multiple-light beam and even by area illumination. The light detectors (also referred to as light sensors) can include discrete detectors as well as detector arrays.
There is a greater emphasis on the throughput of inspection devices and accordingly on the throughput of scanners, as the design rules for semiconductors rapidly shrink without a corresponding decrease of the inspection sequence time period or the overall size of semiconductor dies or wafers.
The throughput of optical inspection systems were increased by using area illumination or multiple beam illumination. U.S. Pat. No. 6,671,042 of Almogy, U.S. Pat. No. 6,639,201 of Almogy et al., U.S. Pat. Nos. 6,578,961 and 6,208,411 of Vaez-Iravani and U.S. Pat. No. 6,248,988 of Krantz, which are incorporated herein by reference, describe state of the art inspection systems.
There is a need to further increase the throughput of optical inspection systems, and especially cost effective optical inspection systems.